How do I limit Nginx/PHP-FPM to 1 client connection only?

"How Do I...?"
1

What I’m trying to do:

Hello, I am seeking for Your suggestion on how to allow running a PHP script only once at a time, not for more than 1 persons/clients. Because the PHP script is made to run a python command which fails if attempted to run more than 1 time:

exec("$*** siteSign $site $privatekey --publish 2>&1", $out);

Also it is modifying a .json file (which may also be the problem if done concurrently?):

$f = fopen($users_json, "w");
fwrite($f, $json_out);
fclose($f);

What I’ve already tried:

Not being a PHP developer I spent like one hour trying to talk to AI and figure out how to limit Nginx to only one client.

nginx -v; php -v; lsb_release -d

nginx version: nginx/1.22.1
PHP 8.2.28 (cli) (built: Mar 13 2025 18:21:38) (NTS)
Description:    Debian GNU/Linux 12 (bookworm)

Result:

https://nginx.org/en/docs/ngx_core_module.html#worker_processes set to 1
https://nginx.org/en/docs/ngx_core_module.html#multi_accept set to off
https://nginx.org/en/docs/ngx_core_module.html#worker_connections set to 1

edited in my /etc/nginx/nginx.conf After saving, I have ran “nginx -t”. It may complain that “1 worker_connections are not enough for 4 listening sockets”.
It means that I may have open 4 HTTP/s ports (443 ipv4, ipv6; 80 ipv4, ipv6).
I have also adjust PHP FPM settings in /etc/php/*/fpm/pool.d/www.conf

pm = ondemand
pm.max_children = 1
pm.start_servers = 1
pm.min_spare_servers = 1
pm.max_spare_servers = 1
pm.max_requests = 1

In my case the error log still shown sockets errors when visiting all 2 .php files, until I have raised worker_connections to 7 (6 not worked - Error 500).
So it looks to me like I have managed to limit clients to 1 or no?

Or please can you suggests more simple and better way to handle this, considering i am total newbie to Nginx and not a PHP developer?

2

The most direct solution is to implement file locking in your PHP script:

// Define a lock file
$lock_file = "/tmp/my_script.lock";

// Try to get an exclusive lock
$lock = fopen($lock_file, "w");
if (!flock($lock, LOCK_EX | LOCK_NB)) {
    // Could not get lock - script is already running
    echo "Script is already running. Please try again later.";
    exit(1);
}

// Now we have the lock, run your code
try {
    // Your existing code here
    exec("$*** siteSign $site $privatekey --publish 2>&1", $out);
    
    // JSON file operations with proper locking
    $f = fopen($users_json, "w");
    fwrite($f, $json_out);
    fclose($f);
} finally {
    // Release the lock
    flock($lock, LOCK_UN);
    fclose($lock);
    @unlink($lock_file); // Optional: remove the lock file
}
1 Like